Temporal lobe epilepsy is the most common focal epilepsy in adolescents and adults, and the most frequent indication for epilepsy surgery. Mesial temporal lobe epilepsy (MTLE) often originates from the hippocampus, which is implicated in declarative memory function. A clinical trial in patients with intractable MTLE showed that temporal lobectomy is superior to continued medical therapy in achieving seizure freedom. However, resection is generally eschewed if pre-surgical evaluation predicts functional deficits. Additionally, more than half of all intractable patients are not candidates for surgical resection. The risk of memory decline after hippocampal resection depends on the structural integrity of the hippocampus and its degree of contribution to memory function prior to surgery. A non-lesional, language dominant hippocampus and good preoperative memory function often exclude MTLE patients from temporal lobectomy because of the high-risk of postoperative memory decline. This underlies the need to pursue controlling disabling hippocampal seizures without compromising memory function.
While surgical resection of the temporal lobe is an effective treatment for medically-intractable temporal lobe epilepsy, surgical resection often results in memory impairment. Thus, other approaches including deep brain stimulation (DBS) have been undertaken. DBS in epilepsy has targeted gray matter structures using high frequencies, but has not achieved desired results. Conventional DBS may provide a first stimulation when there is no prediction of an impending seizure but may provide a second altered stimulation based on a prediction of an impending seizure, where the prediction is based on monitoring naturally occurring, organically generated signals. For example, conventional systems may be programmed to detect and record seizure activity based on signals generated naturally in the brain by the brain itself. Conventional systems may also be configured to control stimulation as a function of the detected or recorded seizure activity.
DBS has risen as an effective treatment in patients with movement or psychiatric disorders. The stimulation targets specific areas in the brain, altering the function of circuits or inducing neurogenesis and other plastic changes. DBS has been approved for treatment of Parkinson's disease, essential tremor, dystonia, and obsessive-compulsive disorder, but its success in epilepsy has been limited. Most stimulation trials in epilepsy have used high frequencies.